1. Field of Invention
The present invention relates to an air valve, and more particularly to a multifunctional combination air valve set having three individual orifices and one specific combined function of two of the three independent functions, wherein the independent functions are mid-high rate air vent/admitting (also), high-rate air admitting, and small volumes air release. The unique function is a combination of high-rate air admitting and small volumes air release for substantially dissipation or preventing the down-surge caused by column-separation from occurrence.
2. Description of Related Arts
The conventional combination air release valve usually has a common orifice for both high-rate air venting and high-rate air admitting which does not provide different orifices for air venting and air admitting respectively, which means lacking of independence for both functions. On the other hand, a conventional high-rate air venting orifice usually has a large diameter relatively to the required, while a conventional high-rate air admitting orifice has a smaller diameter relatively to the required and inadequate for air admitting capacity, which might contribute to development of high negative pressure (vacuum). A conventional small volumes release orifice has a relatively small diameter which is normally just 1.6 mm to 4.0 mm, and cannot satisfy the releasing requirement for large diameter pipeline.
When an empty pipeline or container is being filled with water/fluid, the air inside is rapidly discharged through a high-rate large orifice which develops a substantial differential pressure between the upstream and downstream of the orifice (or across the orifice). When this differential pressure reaches a range between 2 kPa and 3 kPa, the float working as the disc of the conventional air valve may be blown-shut to close the orifice by high rate stream around it so as to premature stopping further high-rate air discharge from the pipeline or the container. The consequence is that a substantial amount of air is trapped and remained so that incoming fluid, such as water, is prevented from further flowing into the pipeline or the container, and it cannot be full filled actually. This substantially lowers the conveyance capacity and the performance of the pipeline, and the power efficiency to operate the pipeline. The above-mentioned phenomenon also causes the problems of unstable pressure, elevated risk of corrosion on the part of the pipeline, operation cost increasing and calculation/metering errors in assigning system parameters.
Moreover, when the mid-high rate air venting/admitting orifice of the conventional combination air valve is premature blown shut (closure) by high speed air stream, air trapped in the pipeline or the container may be released through the small orifice, but the entire process requires a prolonged period of time. As a result, it may take a prolonged period of time for initial filling of water in a pipeline system or a container, and this substantially affects the efficiency of the entire pipeline system. This problem worsens when the pipeline system locates in high latitude area where summer is very short.
In order to minimize the differential pressure across the mid-high rate air venting/admitting orifice, a diameter of the orifice thereof is typically designed to be as large as possible. However, as mentioned previously, the same orifice is typically used for mid-high rate air venting and high-rate air admitting. As a result, in order to simultaneously satisfy the requirement of high-rate air admitting and high-rate air venting, the diameter of the high-speed exhaust orifice is typically designed to be larger than what is actually required. The consequence is: although the differential pressure across the mid-high rate air vebting orifice is lowered, the rate at which water flows into the pipeline or the container (initial filling) is accordingly increased, because of the lowering the back-pressure exerted on the front face of filling water column which were developed by the flowing air remained in the system (pipeline or container). If the filling flow rate of the water during the last minutes of the system is too high, the float disc of the combination air valve will be buoyed up hydraulically too quickly to close the high rate air venting orifice and sudden stop the water flowing in the pipeline or the container. Such a sudden stop of the water flow velocity causes a very high transient pressure to be developed upstream the high rate air venting orifice and eventually causes air valve slam and subsequent up-surge (positive water hammer, Δh=a*ΔV/g, surge pressure Δh is proportional to rate of change of flow rate ΔV). This water hammer may eventually damage the pipeline and this is actually the most significant cause of pipeline damages: it is not that the diameter of the mid-high rate air venting orifice is too small for air discharge during filling. On the contrary, the diameter of the mid-high rate air venting orifice is too large. Thus, a dynamically controlled mid-high rate air venting valve is capable of providing an optimal back-pressure and fluid filling rate, and, at the same time avoiding air valve slam and the development of water hammer due to the sudden stopping of fluid flow by the float disc at the last minutes of the system filling.